text: /*  $OpenBSD: qsort.c,v 1.10 2005/08/08 08:05:37 espie Exp $ */
  /*-
   * Copyright (c) 1992, 1993
   *  The Regents of the University of California.  All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. Neither the name of the University nor the names of its contributors
   *    may be used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   */
  
  #include "sys/types.h"
  #include "stdlib.h"
  
  static __inline char    *med3(char *, char *, char *, int ( *)(const void *, const void *));
  static __inline void     swapfunc(char *, char *, int, int);
  
  #define min(a, b)   (a) < (b) ? a : b
  
  /*
   * Qsort routine from Bentley & McIlroy's "Engineering a Sort Function".
   */
  #define swapcode(TYPE, parmi, parmj, n) {       \
      long i = (n) / sizeof (TYPE);           \
      TYPE *pi = (TYPE *) (parmi);            \
      TYPE *pj = (TYPE *) (parmj);            \
      do {                        \
          TYPE    t = *pi;            \
          *pi++ = *pj;                \
          *pj++ = t;              \
          } while (--i > 0);              \
  }
  
  #define SWAPINIT(a, es) swaptype = ((char *)a - (char *)0) % sizeof(long) || \
      es % sizeof(long) ? 2 : es == sizeof(long)? 0 : 1;
  
  static __inline void
  swapfunc(char *a, char *b, int n, int swaptype) {
      if (swaptype <= 1)
          swapcode(long, a, b, n)
          else
              swapcode(char, a, b, n)
          }
  
  #define swap(a, b)                  \
      if (swaptype == 0) {                \
          long t = *(long *)(a);          \
          *(long *)(a) = *(long *)(b);        \
          *(long *)(b) = t;           \
      } else                      \
          swapfunc(a, b, es, swaptype)
  
  #define vecswap(a, b, n)    if ((n) > 0) swapfunc(a, b, n, swaptype)
  
  static __inline char *
  med3(char *a, char *b, char *c, int (*cmp)(const void *, const void *)) {
      return cmp(a, b) < 0 ?
             (cmp(b, c) < 0 ? b : (cmp(a, c) < 0 ? c : a ))
             :(cmp(b, c) > 0 ? b : (cmp(a, c) < 0 ? a : c ));
  }
  
  void
  qsort(void *aa, size_t n, size_t es, int (*cmp)(const void *, const void *)) {
      char *pa, *pb, *pc, *pd, *pl, *pm, *pn;
      int d, r, swaptype, swap_cnt;
      char *a = aa;
  
  loop:
      SWAPINIT(a, es);
      swap_cnt = 0;
      if (n < 7) {
          for (pm = (char *)a + es; pm < (char *) a + n * es; pm += es)
              for (pl = pm; pl > (char *) a && cmp(pl - es, pl) > 0;
                      pl -= es)
                  swap(pl, pl - es);
          return;
      }
      pm = (char *)a + (n / 2) * es;
      if (n > 7) {
          pl = (char *)a;
          pn = (char *)a + (n - 1) * es;
          if (n > 40) {
              d = (n / 8) * es;
              pl = med3(pl, pl + d, pl + 2 * d, cmp);
              pm = med3(pm - d, pm, pm + d, cmp);
              pn = med3(pn - 2 * d, pn - d, pn, cmp);
          }
          pm = med3(pl, pm, pn, cmp);
      }
      swap(a, pm);
      pa = pb = (char *)a + es;
  
      pc = pd = (char *)a + (n - 1) * es;
      for (;;) {
          while (pb <= pc && (r = cmp(pb, a)) <= 0) {
              if (r == 0) {
                  swap_cnt = 1;
                  swap(pa, pb);
                  pa += es;
              }
              pb += es;
          }
          while (pb <= pc && (r = cmp(pc, a)) >= 0) {
              if (r == 0) {
                  swap_cnt = 1;
                  swap(pc, pd);
                  pd -= es;
              }
              pc -= es;
          }
          if (pb > pc)
              break;
          swap(pb, pc);
          swap_cnt = 1;
          pb += es;
          pc -= es;
      }
      if (swap_cnt == 0) {  /* Switch to insertion sort */
          for (pm = (char *) a + es; pm < (char *) a + n * es; pm += es)
              for (pl = pm; pl > (char *) a && cmp(pl - es, pl) > 0;
                      pl -= es)
                  swap(pl, pl - es);
          return;
      }
  
      pn = (char *)a + n * es;
      r = min(pa - (char *)a, pb - pa);
      vecswap(a, pb - r, r);
      r = min(pd - pc, pn - pd - (int)es);
      vecswap(pb, pn - r, r);
      if ((r = pb - pa) > (int)es)
          qsort(a, r / es, es, cmp);
      if ((r = pd - pc) > (int)es) {
          /* Iterate rather than recurse to save stack space */
          a = pn - r;
          n = r / es;
          goto loop;
      }
      /* qsort(pn - r, r / es, es, cmp); */
  }
  